[meteorite-list] Ancient Meteorite Found in Sweden Quarry Is In A Class of Its Own

[Ron Baalke]

http://scitation.aip.org/content/aip/magazine/physicstoday/news/10.1063/PT.5.7275

Ancient meteorite is in a class of its own

A space rock found in a Swedish quarry suggests that the kinds of meteors 
raining down on Earth have changed over time.

Andrew Grant
Physics Today
14 June 2016

More than four-fifths of the asteroids recovered on Earth as meteorites 
are ordinary chondrites - iron-poor rocks that contain small round grains, 
or chondrules. Over the past two decades, Birger Schmitz at Lund University 
in Sweden and his colleagues have assembled evidence that a subset of 
ordinary chondrites, known as L chondrites, are pieces of a single large 
asteroid that was shattered in a collision about 470 million years ago.

Now Schmitz and his team have conducted a detailed analysis of a peculiar 
meteorite that has the age of an L chondrite but not the composition. 
sterplana 065 (pictured below) was discovered in 2011 at the Thorsberg 
quarry in southern Sweden, where workers for a company that produces limestone 
floors have uncovered more than 100 L chondrites in ancient sediment. 
Compared with the L chondrites, Ost 65 contains far less oxygen-17 than 
it should based on its concentration of chromium-54; the ratio of the 
two isotopes is used to classify meteorites. The quirky space rock also 
lacks certain minerals and the chondrule texture that distinguish chondrites.

The researchers argue that the discovery of this one anomalous specimen 
out of the more than 52 000 meteorites classified worldwide has major 
implications. Schmitz and his colleagues propose that Ost 65 is the first 
evidence of an extinct meteorite, which no longer falls to Earth yet is 
representative of the kinds of rocks that exist elsewhere in the solar 
system. The researchers go further and suggest, based on the meteorite's 
age, that Ost 65 is a fragment of the object that slammed into the parent 
body of the L chondrites. (B. Schmitz et al., Nat. Comm. 7, 11851, 2016.)